Optimum design of a nondissipative snubber

A simple and cost advantageous PWM flyback converter with a nondissipative snubber for microwave heating application was analysed, optimised and tested. There is an optimum snubber capacitor value providing minimum overall losses which depends not only an the converter components quantities but on the transistor parameters as well and therefore requires a thorough analysis with minimum simplifications. Both the losses and surge voltage quantities are only slightly affected by the snubber capacitor value within a quite wide region of C and this fact could be used for experimental circuit optimisation. The experimental waveforms have showed that IGBT transistor performance during turn-off and turn-on transitions can be modelled by linearly decreasing current and voltage sources. The nondissipative snubber can decrease substantially the turn off transistor losses and in the case of IGBTs can extend their operating frequency up to several tens of kHz for the fast series and to one hundred kHz for the ultrafast ones